Method of forming a prefabricated stair unit



Feb. 14, 1961 K. I. FORSSELL 2,971,238

METHOD OF FORMING A PREFABRICATED sum UNIT Filed Dec. 10, 1953 4 Sheets-Sheet 1 7 FIG.1

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METHOD OF FORMING A PREFABRICATED STAIR UNIT Filed D80. 10. 1953 4 Sheets-Sheet 2 Fl Gib 2,971,238 METHOD OF FORMING A PREFABRICATED STAIR UNIT Feb. 14, 1961 K. I. FORSSELL Filed Dec.

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Feb. 14, 1961 K. I. FORSSELL ,971,238

METHOD OF FORMINGA PREFABRICATED STAIR UNIT Filed Dec. 10, 1953 4Sheets-Sheet 4 FIG.3

Ker! Qn Forss ell lNvENToQ Unitd tates Pat n METHOD OF FORMING A PREFABRICATED STAIR UNIT Karl Ivan ForsselLNorberg, Sweden Filed Dec. 10, 1953, Ser. No. 397,389

2 Claims. (Cl. 25-154) form a mould, which then receives reinforced, concrete...

for example in difierent layers with internal thermal and acoustic insulating material, for example clinkers, the concrete then being formed against risers and treads of. marble, other natural stone or, artificial stone loosely laid into the mould formed by the stringers, treads and risers before the casting, the exposed surfaces of said risers and treads being ground or otherwise finished in advance.

Various objects, features and advantages of the invention will become apparent upon reading the. following specification together with the accompanying drawing forming a part hereof.

Referring to the drawing:

Figure 1 is a sectional view in elevation showing a single stair unit in accordance with the invention extending between two floors at different levels.

Fig. 1a is a side elevational viewof a stringer in accordance with the invention.

Fig. 1b is a view of the reverse, side of the. stringer shown in Fig. 1a and showing the same resting in alterizontal position.

Fig. 1c is a perspective view of a mold forming a part of the invention.

Figure 2 is a side view in elevation showing two stair units in accordance with the invention extending to a common support, the support being located between two floors at different levels.

Figure 3 is an elevational view of the common support shown in Fig. 2.

Figure 4 is an end view of the support shown in Fig. 3.

Figure 5 is a bottom perspective view of a modified form of support as shown in Figs. 3 and 4.

Referring now to the drawings the reference numeral 1 designates a runner or stringer, 2 designates treads of marble, 3 designates risers of marble, 4 designates an inner, reinforced, comparatively thin concrete layer, 5 designates thermally and acoustically insulative and weight reducing filling of clinkers or the like, 6 designates a lower, plain, relatively thin, and reinforced concrete layer, and 7 and 7a designate upper and lower floor levels respectively. The stair units are manufactured in the following way:

The lateral risers or stringers 1 which are the principal load carrying part of the stair unit are cast separately, preferably of artificial stone and of the same colour as the risers and the treads, for example like marble or of some other colour. The mould in which the stringers are cast, is shaped in such a manner that the finished runners or stringers will be provided at their inner lateral surfaces with stop eges for the application of the loose risers and treads for the next casting operation which is carried out using reinforced concrete. In Fig. 1 the reinforcing bars or other reinforcing members are designated by thick, dashed lines 8, 9 and 10. Reinforcement is laid in the stringer to an extent sufiicient to provide the desired load carrying capacity. Furthermore strap irons 32 are bent out at the inside of the stringer, there being about ten. in each stringer and placed in such a manner that they are supported immediately below the riser and the tread. Before the casting these irons are connected to the reinforcing body formed of the reinforcing rods by welding or in some other way, so that a solid body is obtained. Two stringers 1 are placed in parallel relationship to each other as shown in Fig. 10 which perspectively illustrates the mould itself practically ready to receve concrete, i.e. the tread plates 2 and riser plates 3 have been put in place, in order to serve as bottom of the mould, while the stringers 1 serve as sides of the same. A piece of board 34 may be used as end wall during the casting. The plates 2 and 3 are disposed in correct position thanks to the edges 30, 31 of grooves in the stringers whichedges constitute the stop edges mentioned above.

When setting the elements 1, 2 and 3 together I lay down the plates 2 and 3 on the support, and place the edges 30, 31, and the lower edge of each plate 2 to rest Then I connect the stringers.

in corresponding grooves. fixedly to each other by means of the reinforcing rods 32a which are joined to the straps 32 by welding or the like, whereafter I lay out reinforcing rods 32b after having filled the step cavities as mentioned above and spread out a thin first layer 4 of concrete. Then I fill the rest of the mould with concrete. The last step of the casting is to vibrate the whole cast body and to surface vibrate and polish the upward facing underside, so that a fine finished surface is obtained.

Owing to the fact that the stringers are manufactured separately they can be surface ground before being castin, for example by means of a usual surface grinding machine, which. is. easier before than after the casting-in.

Stairs of other shapes can of course be manufactured in accordance with the invention. Thus, the invention can be utilized for connecting prefrabricated single-flight stair units manufactured as described above and for forming single-flight stair units preferably to be installed with one stringer along a wall and the other stringer free. In certain houses, for example point houses or star-shaped houses, the stairs are placed in the middle of the house, which means that all single-flight stairs, i.e. the stair of each flat, are preferably built up as a unit. The purpose of this part of the invention is to facilitate such an arrangement, the stringer of one side being preferably but not necessarily freely mounted.

This aspect of the invention is characterized in that the individual stair units or single-flight stairs, are each provided at one or both of its end portions with a half tread, terminating the end of the stair unit, and with an end recess running transversely of the stair unit, are mounted together end to end, so that the recesses meet forming a transverse groove opening downwardly at the underside of the combined stair units, said groove being fitted to a projecting beam which is rigidly connected to the wall at a suitable point and projecting outwardly at right angles from said wall, so that the abutting stair unit ends, when fixed in relation to each other, rest on the beam, whereby the adjacent half treads together form a full tread of normal size.

In Figs. 25 the reference numerals 12 and 13 designate two abuttingly connected prefabricated, equally broad single-flight stair units of the kind which are preferably made in accordance with the method described above. Each of these single-flight stair units comprises a half tread 2a and 27) respectively and an end recess 14' and 15 disposed below each half tread 2a and 2b r'espec tively and at the abutting ends of the stair units, facing each other and extending transversely across the end of tion to each other by simply resting on the beam 17;

Each of the other short ends of the stairs can, as shown in Fig. 2, be placed against transverse supporting beams 18 and 19 respectively, or it can be connected to another stair unit in the same flight as described above. In the embodiment shown, the projecting beam 17 is made of concrete with substantially square, rectangular, pentagonal, or hexagonal cross section, and as shown in Figs. 3 and 4 it is built into a brick wall by means of a comparatively short concrete column 20 formed integrally with the projecting beam 17, said concrete column being .attached to the seams of the brick wall by means of horizontally projecting lateral reinforcing rods 21 (Fig. 4). The projecting beam 17 is preferably of a length which equals approximately the Width of the stairs 12 and 13 and is provided at its free end with an upwardly bent iron 22 intended to provide additional support for a hand rail (not shown) when a hand rail is mounted on the free stringers of the stairs 12 and 13. 35

Of course the details described above can be varied within the scope of the invention.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1'. The method of forming a prefabricated stair unit comprising the steps of separately forming a pair of lateral stringer members with mutually corresponding and facing means to support intermediate tread and riser members, finishing those surfaces of said stringers which will be exposed in the completed unit, placing said prefinished stringers in an inverted and spaced position on a support, placing prefinished tread and riser members in inverted tread and riser position between said stringers 4 v and with their ends in supported engagement with the corresponding support means on the opposing faces of said stringers, positioning reinforcing members along said stringers and along the backs of said tread and riser members, securing said reinforcing members together, pouring a thin layer of concrete between said stringers and over said reinforcing elements, treads and risers to tie them together into a single unit, allowing said thin layer to harden, filling the angles between the tread and riser members with insulating material, and pouring a final layer of concrete over the entire exposed surface of the unit to secure said insulation in position and provide additional supportfor said unit.

2. The method of forming a prefrabricated stair unit comprising the steps of separately forming a pair of lateral stringer members with mutually corresponding and facing means to support intermediate tread and riser members and with inwardly directed strap members cast therein, finishing those surfaces of said stringers which will be exposed in the completed unit, placingsaid prefinished stringers in an inverted and spaced position on a said stringers, positioning reinforcing members along said stringers and along the backs of said tread and riser members, securing said reinforcing memberstogether,

' securing said straps to said reinforcing members, pouring a layer of concrete between said stringers and over said reinforcing elements, treads and risers to tie them together into a single unit.

' References Cited in the file of this patent UNITED STATES PATENTS,

987,737 Oman Mar. 28, 1911 1,051,753 Olfe Jan. 28, 1913 1,064,050 .Brooks June 10,1913 2,093,763 Lee Sept. 21, 1937 2,190,801 Otto Feb. 20, 1940 2,289,439 Kogl July .14, 1942 2,331,701 Kogl Oct. 12, 1943' 2,377,944 Kohlhass July 12, 1945 FOREIGN PATENTS 134,352 Sweden Jan. 22, 1952 Sweden Feb. 5, 

